Electromagnetism - The Burns Home Page

03/12/2010
Electromagnetism Review
EMF
Electromagnetism Review
Recall
EMF induced in a Moving Conductor
Force of Magnetic Field on Current
BLv
m
1.2T 2.0m7
s
17V
X X X X X X X X X X X
X X X X X X X X X X X
X X X X X X X X X X X
X X X X X X X X X X X
X X X X X X X X X X X
• Force on 1 moving charge:
‣ F = q v B sin()
‣ Out of the page (RHR)
• Force on many moving charges:
‣ F = (q/t)(vt)B sin()
= I L B sin()
+
‣Out of the page!
+
v
+ + +
v
L = vt
B
I = q/t
distance
Torque on Current Loop in B field
W
d
a
• F
L
Force on sections B-C and A-D: F = IBW
Torque on loop is t = L F sin(f) = ILWB sin(f)
Torque is
I
(length x width = area)
c
F
X
b
B
t = I A B sin(f)
LW = A
F
d
f
a
b
c
F
Understanding: Torque on
Current Loop
What is the torque on the loop below?
1
2
3
t < IAB
t = IAB
t > IAB
t = 0
x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x
x x x x x x x x x x x x x x x x
7